Rear diff trouble


New Member
May 9, 2019
Farmington, mn
Last summer my girlfriend put my 04, automatic v6 mustang into revease in a neutral prank gone wrong. It killed the car on spot and I restarted it and drove it 2 blocks home and then parked it for the winter. I started it last week and drove about 20 ft. When it started grinding on turns from the rear and knocking real hard on occasion. I'm thinking the rear diff is the problem, but do not want to replace it if the trans or driveshaft took a big hit. I still have to pop the rear diff cover to see what's up. Any other ideas or views?
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SN Certified Technician
Aug 14, 2009
Houston Texas
Just wondering. What have you done to rule out something simple like bad U-joints?

If this were my car I would also be looking at the slip yoke. As well as all of the suspension points that might allow the axle to rotate the pinion up/down.

If it does turn out to be a problem inside the rear end itself almost anything wrong with a rear end (short of major breakage) can be repaired with a rebuild kit. The Ford rear end is a very "serviceable" unit.

I also thought the the transmission controller would not let an automatic go into reverse while going forward.

Have you considered the GF 2.0 upgrade? :)
Dec 30, 2018
Medford, OR
the GF 2.0 would definitely be your most cost effective way to go lmao :D

but I second starting at the simplest solution and working up from there. However if you haven't serviced your diff a fluid change can do wonders..... however not if you need a rebuild because then you would be doing the fluids anyways

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